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I have a 1973 Beetle with a lowered compression stock engine to make it run cooler.
It was getting about 17.5 MPG city. The MPG has dropped to about 12 MPG.
It has less than 30,000 miles on the engine.

Could it be caused by sticky valves or lifters?
I saw a way to check for sticky valve on youtube by warming it up and holding a piece of paper at the exhaust pipe. If it sucks the exhaust air in then you have a sticky valve they said. I have not tried the paper test yet.
The reason I ask is because it does not get driven much. Usually I just start it up once in awhile.

I was also thinking it might be caused by a weak ignition coil or the Pertronix I is getting old. I had installed both of those about 18 years ago.

I replaced the blue Bosch 3 ohm coil and the Pertronix I with a black Pertronix 3 ohm coil and a Pertronix II drop in ignition.

I replaced the spark plugs with NGK B5HS copper core plugs and set the gap to .028 IN. The old plugs had kind of orange brown tan deposits on them so, I adjusted the carb air:fuel mixture a little leaner.
I let it idle for an hour to warm it up really good.
I saw on youtube that by letting it idle for two hours you can sometimes free a sticky valve.

It runs really smooth and seems to have plenty of power .

Any help is appreciated! TIA!

idling for hours definitely correlates with abismal fuel consumption

I checked my tire air pressure.
The right rear had 20 p.s.i. I didn't check the rest.
The decal on the glove box door says 27 p.s.i. rear and 17 p.s.i. in front.
So, Sent off for a new Rhino dial tire gauge. I will air up the tires and re-check my MPG figures later.

Jim Ed wrote: ↑Mon Nov 19, 2018 2:57 pm I have a 1973 Beetle with a lowered compression stock engine to make it run cooler.
It was getting about 17.5 MPG city. The MPG has dropped to about 12 MPG.

When you lower the compression ratio, the efficiency also goes down. That's why your fuel consumption went up.
Also, your lower compression engine didn't run cooler, right?

Yes it runs cooler.
Re: When you lower the compression ratio, the efficiency also goes down. That's why your fuel consumption went up.
Also, your lower compression engine didn't run cooler, right?

I think I discovered the cause of the drop in mpg.
Yesterday, after I started it up to let it idle a bit I shut if off.
While sitting behind the Beetle I thought I smelled gas vapor.
I opened the deck lid and notice that the fuel line from the carb was wet.
It apparently had been leaking gas.
So, check the engine compartment before and after you start it up.
I will change that hose today.

I replaced the OEM German hose with Gates' Barricade 1/4 INCH fuel hose. Now I don't have to be concerned with ethanol gas eating up the hose.
I also installed a Brosol fuel pump from WolfsburgWest. It has the clips on the pivot pin to help to keep it from working itself out. I started it up. It runs like new. Now I am waiting for a Wix fuel filter with 1/4 inch ends.